Transmission is a vital component in multi-speed electric vehicles or power tools. The transmission system typically accounts for about half of the production cost. Thus research on speed changing apparatus has been a key task for makers of electric vehicles or power tools. In an electric vehicle for example, a good transmission system enables riders to change the revolution ratio in response to the surrounding environment so as to attain an appropriate speed or torque.
For multispeed electric vehicles, planetary gear sets are commonly used in transmission system. In a planetary internal transmission system, a planetary gear train is used as the principal part of speeding changing apparatus where the apparatus is installed in a rear wheel hub shell to achieve varying revolution ratios by changing the gear ratio of the planetary gear train through different input, output and stationary pieces.
An internal transmission using a planetary gear train as the principal part of its speed changing apparatus offers the following advantages. Firstly, with a small size and precise construction, its installation and use are less confined by the narrow space in the rear wheel hub shell. Secondly, the gear shifting process works stably so that it will not cause the chain to engage different chain wheels, thereby effectively improving the drawback of chain derailment and increasing the transmission efficiency. Thirdly, the speed changing apparatus is protected by the external housing of the wheel hub shell from the outside environment, which could prolong its service life. Fourthly, the speed changing apparatus is installed inside the wheel hub shell so that not as much noise as an external transmission would be produced during the gearshift.
According to the transmission principle of a planetary gear train, the sun gear, planet gear (or carrier arm) and ring gear each have a shaft and these three gears revolve around one another. At different gears, one of the three gear shafts would stays stationary without turning, another is a driving shaft, and still another is an output shaft. Different combinations result in gear ratios needed in different revolutions for deceleration, acceleration or reverse. Six possible combinations are shown as below.
Combination123456Sun gearStation-OutputStation-DrivingOutputDrivingaryaryplanet pinionsDrivingDrivingOutputOutputStation-Station-(or carrier arm)aryaryRing gearOutputStation-DrivingStation-DrivingOutputaryary
The present invention focuses on the internal speed changing apparatus of a planetary gear train for wheeled or electric vehicles. Additionally, heightened awareness to environmental protection has made electric bicycles and vehicles popular in recent years. The majority of electric bicycles and vehicles on the market today are equipped with an internal transmission system. Thus, internal transmission has gradually become a focus of research efforts for large vehicle makers.